Effect of aging on the crack propagation behavior of A356 alloy under resonant vibration

In this study, A356 Al-Si-Mg cast alloy was aged to various conditions to e xplore the crack propagation behavior under resonant vibration. The results of all aging conditions indicate that the cracks in the eutectic regions a dvance by linking with broken silicon particles or decohered particle/matri x interfaces. Crack branching is severe for the peak-aged and overaged spec imens in which the cracks tend to propagate in the eutectic regions. These specimens exhibit increasing crack propagation resistance with increasing y ield strength and microhardness. For the naturally aged and underaged speci mens, the crack propagation resistance also increases with increasing stren gth and hardness. Crack tortuosity is large for these specimens in which th e cracks in alpha-matrix proceed by meandering along slip bands. Deviation of the test frequency from the resonant frequency occurs when the crack len gth becomes critical. A change in the aging condition has no apparent effec t on this critical crack length.